1. Field of the Invention
The present invention is in the field of processed security paper and specifically relates to a paper bearing a hidden but visible mark that is not reproducible and which thereby verifies the paper as an original document.
2. The Prior Art
So far as is known, the validation mark of the present invention is unique and can be distinguished from other means for achieving the same result.
Perhaps the earliest validation mark was the watermark, which also does not reproduce, even on the best contemporary copying machines. However, a watermark is usually viewed perpendicular to the paper by light transmitted through the paper, and when viewed in this manner it has the form of a lighter mark on a darker background.
It is also well known to print on a sheet of paper a high resolution background pattern, called a pantograph, that is somewhat difficult to copy and that would normally be destroyed if an attempt is made to alter the original.
In U.S. Pat. No. 4,796,921, Neiman describes the expedient of printing a hidden message onto a sheet of paper using ink that is the same color as the sheet and which is opaque. The message is read by illuminating the back of the sheet, and the message always consists of darker marks on a lighter background.
In U.S. Pat. No. 4,534,398, Crane describes a type of security paper in which optically active devices which have been secured on the surface of a carrier paper are applied to the surface of a base web during dewatering of the base web in the paper manufacturing process. The optically active devices display their optically active properties in reflectance when there are changes in the angle of the incident light with respect to the eye of the viewer.
In U.S. Pat. No. 4,151,666, Raphael, et al. show the use of an optically diffuse reflector integrated with a bond or seal existing between a protective sheet and the information-bearing surface of a laminated document, such as an identification card. The optically diffuse pigment is dispersed in a carrier medium and printed on an adhesive layer that becomes the bond when the identification card is laminated.
A number of other patents are concerned with the unauthorized copying of original documents through the use of modern computer scanners or high quality color copying machines. Typical examples of such patents are the following U.S. patents of Mowry, Jr. et al.: U.S. Pat. Nos. 4,210,346; 4,227,720; 4,265,469; 4,310,180; and 4,341,404. In these patents, typically a cancellation phrase or message is printed in a concealed manner on the face of the protected document so that it cannot be seen on the original document, but the cancellation phrase is produced clearly on any copies made from the original document. It is seen that these techniques are directed against the reproduction of a document; in contrast, the purpose of the present invention is to permit rapid visual validation of an original document.